Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$47.29	5.813%	$50.039	$50.04	$50.05	$50.00
Purchase #2	$176.56	6.670%	$188.3366	$188.34	$188.35	$188.30
Purchase #3	$69.32	5.193%	$72.9198	$72.92	$72.90	$72.90
Purchase #4	$82.41	3.501%	$85.2952	$85.30	$85.30	$85.30
Purchase #5	$84.84	5.260%	$89.3026	$89.30	$89.30	$89.30
Purchase #6	$234.25	9.381%	$256.225	$256.23	$256.25	$256.20
Purchase #7	$161.67	11.596%	$180.4173	$180.42	$180.40	$180.40
7 purchase totals =	$856.34		$922.5355	$922.55	$922.55	$922.40